It is fairly well established that many pathological conditions, such as infections, cancer, autoimmune disorders, etc., are characterized by the inappropriate expression of certain molecules. These molecules thus serve as "markers" for a particular pathological or abnormal condition. Apart from their use as diagnostic "targets", i.e., materials to be identified to diagnose these abnormal conditions, the molecules serve as reagents which can be used to generate diagnostic and/or therapeutic agents. A by no means limiting example of this is the use of cancer markers to produce antibodies specific to a particular marker. Yet another non-limiting example is the use of a peptide which complexes with an MHC molecule, to generate cytolytic T cells against abnormal cells.
Preparation of such materials, of course, presupposes a source of the reagents used to generate these. Purification from cells is one laborious, far from sure method of doing so. Another preferred method is the isolation of nucleic acid molecules which encode a particular marker, followed by the use of the isolated encoding nucleic acid molecule to express the desired protein molecule.
To date, two strategies have been employed for the detection of such antigens, in e.g., human tumors. These will be referred to as the genetic approach and the biochemical approach. The genetic approach is exemplified by, e.g., dePlaen et al., Proc. Natl. Sci. USA 85:2275 (1988), incorporated by reference. In this approach, several hundred pools of plasmids of a cDNA library obtained from a tumor are transfected into recipient cells, such as COS cells, or into antigen-negative variants of tumor cell lines. Transfectants are screened for the expression of tumor antigens via their ability to provoke reactions by anti-tumor cytolytic T cell clones. The biochemical approach, exemplified by, e.g., Mandelboim, et al., Nature 369:69 (1994) incorporated by reference, is based on acidic elution of peptides which have bound to MHC-class I molecules of tumor cells, followed by reversed-phase high performance liquid chromatography (HPLC). Antigenic peptides are identified after they bind to empty MHC-class I molecules of mutant cell lines, defective in antigen processing, and induce specific reactions with cytotoxic T-lymphocytes. These reactions include induction of cytolytic T cell lines (CTLs) proliferation tumor necrosis factor (TNF) release, and lysis of target cells, measurable in an MTT assay, or a .sup.51 Cr release assay.
These two approaches to the molecular definition of antigens have the following disadvantages: first, they are enormously cumbersome, time-consuming and expensive; second, they depend on the establishment of CTLs with predefined specificity; and third, their relevance in vivo for the course of the pathology of disease in question has not been proven, as the respective CTLs can be obtained not only from patients with the respective disease, but also from healthy individuals, depending on their T cell repertoire.
The problems inherent to the two known approaches for the identification and molecular definition of antigens is best demonstrated by the fact that both methods have, so far, succeeded in defining only very few new antigens in human tumors. See, e.g., van der Bruggen et al., Science 254:1643-1647 (1991); Richard et al., J. Exp. Med. 178:489-495 (1993); Coulie, et al., J. Exp. Med. 180:35-42 (1994); Kawakami, et al., Proc. Natl. Acad. Sci. USA 91:3515-3519 (1994).
Further, the methodologies supra described rely on the availability of established, permanent cell lines of the cancer type under consideration. It is very difficult to establish cell lines from certain cancer types, as is shown by, e.g., Oettgen, et al., Immunol. Allerg. Clin. North. Am. 10:607-637 (1990). It is also known that some epithelial cell type cancers are poorly susceptible to CTLs in vitro, thus precluding routine analysis. These problems have stimulated the art to develop additional methodologies for identifying cancer associated antigens.
One key methodology is described by Sahin, et al., Proc. Natl. Acad. Sci. USA 92:11810-11913 (1995), incorporated by reference. Also, see U.S. patent applications Ser. No. 08/580,980, now U.S. Pat. No. 5,698,396 and application Ser. No. 08/479,328, filed on Jun. 7, 1995 and Jan. 3, 1996, respectively. All three of these references are incorporated by reference. To summarize, the method involves the expression of cDNA libraries in a prokaryotic host. (The libraries are secured from a tumor sample). The expressed libraries are then immunoscreened with absorbed and diluted sera, in order to detect those antigens which elicit high titer humoral responses. This methodology is known as the SEREX method ("Serological identification of antigens by Recombinant Expression Cloning"). The methodology has been employed to confirm expression of previously identified tumor associated antigens, as well as to detect new ones. See the above referenced patent applications and Sahin, et al., supra, as well as Crew, et al., EMBO J 144:2333-2340 (1995).
The SEREX methodology has been applied to esophageal cancer samples, and an esophageal cancer associated antigen has now been identified, and its encoding nucleic acid molecule isolated and cloned, as per U.S. patent application Ser. No. 08/725,182, filed Oct. 3, 1996, incorporated by reference herein.
The relationship between some of the tumor associated genes and a triad of genes, known as the SSX genes, is under investigation. See Sahin, et al., supra; and Tureci, et al., Cancer Res 56:4766-4772 (1996). One of these SSX genes, referred to as SSX2, was identified, at first, as one of two genes involved in a chromosomal translocation event (t(X; 18)(p 11.2; q 11.2)), which is present in 70% of synovial sarcomas. See Clark, et al., Nature Genetics 7:502-508 (1994); Crew et al., EMBO J 14:2333-2340 (1995). This gene was later found to be expressed in a number of tumor cells, and is now considered to be a tumor associated antigen referred to as HOM-MEL40 by Tureci, et al, supra. Its expression to date has been observed in cancer cells, and normal testis only. This parallels other members of the "CT" family of tumor antigens, since they are expressed only in cancer and testis cells. Crew et al. also isolated and cloned the SSX1 gene, which has 89% nucleotide sequence homology with SSX2. See Crew et al., supra. Additional work directed to the identification of SSX genes has resulted in the identification of SSX3, as is described by DeLeeuw, et al., Cytogenet. Genet 73:179-183 (1996). The fact that SSX presentation parallels other CT antigens suggested to the inventors that other SSX genes might be isolated.
Application of a modification of the SEREX technology described supra has been used, together with other techniques, to clone two, additional SSX genes, referred to as SSX4 and SSX5 as well as an alternate splice variant of the SSX4 gene. This work is described in U.S. Ser. No. 08/851,138, filed May 5, 1997, incorporated by reference, as well as by Chen, et al., Proc. Natl. Acad. Sci USA 94:1914-1918 (1997), also incorporated by reference.
The fact that many markers were found in both normal testis and tumor cells, but not other normal cells, suggested that further investigation in this area might uncover additional related molecules. The diversity of those discovered so far, however, did not provide any guidance as to the characteristics of the additional molecules which might be found.
Most of the work prior to the invention disclosed herein, used cDNA libraries obtained from cancer cells. As will be developed herein, it has now been shown that such molecules can also be determined using a non-transformed, or normal cell source for the cDNA libraries previously obtained from cancer cells. This is quite surprising, as it might well be assumed that tumor markers are expressed only in tumor cells. This has now been shown to not be the case. Exemplary of a normal cell library which can be used is a testis cell library screened against various serum samples, such as autologous serum.
The SEREX methodology, as described supra, has proven to be very useful in identifying molecules of interest. The inventors have found, however, that it is not an ideal method when short cDNA molecules are the ones of interest in a given library. One aspect of the invention described herein is a method for identifying short cDNA molecules which are of interest in connection with pathologies of the type discussed herein.
Synaptonemal complex protein 1 ("SCP1" hereafter) is a protein involved in the meiotic prophase of spermatocytes. The gene which encodes murine SCP1 has been mapped to chromosome 1p.12-p.13. See Sage, et al, Biochem. Biophys. Acta 1263:258-260 (1995) incorporated by reference. The human form of SCP1 has been reported to be expressed only in testis. See Meuwissen, et al, EMBO J 11:5091-5100 (1992), incorporated by reference.
Meuwissen et al, supra describe SCP1 protein as a major component of the synaptonemal complex, a tripartite, macromolecular assembly which is formed between homologous chromosomes during meiotic prophase. See Wettstein, et al, Annu. Rev. Genet 3:331-413 (1984); Heyting, et al, Genome 31:81-89 (1986). More details of the protein may be found e.g., in Meuwissen, et al, Genomics 37:101-106 (1997); Gillies, et al, Curr. Trac. Lab. Carlsberg 40:135-161 (1975); Schmekel, et al, Exp. Cell Res 226:20-30 (1996); Moses, et al, Symp. Soc. Exp. Biol. 38:245.gtoreq.270 (1984); Carpenter, Bioessays 6:232-236 (1987); Loidl, et al, Genome 33:759-778 (1990); Moens, Bioessays 16:101-106 (1994); Roeder, Trends Genet 6:385-389 (1990).
The location of the gene for SCP1 is different than that for all previously identified cancer testis antigens (CTAs), which map to the X chromosome.
It has been found, that SCP1 is expressed in tumor cells, especially in renal cell carcinomas, gliomas, and breast carcinomas, but not in normal cells except for testis. Hence, it serves as a CTA but differs in that it possesses strong expression not only in melanoma, but in those tumor types listed supra.
This is significant in terms of both diagnostic and therapeutic approaches to transformed cells, as will be seen from the disclosure which follows. The fact that the molecule is also involved in normal meiosis suggests an important correlation between the molecule, chromosomal replication, cell division, and the onset of oncogenesis.